Extra weight comes with more knee pain, stiffness

NEW YORK (Reuters Health) - People who put on weight are more likely to develop knee pain than those who stay the same or lose weight, says a new study.

People who shed pounds saw only a modest improvement in knee pain, however, researchers from Monash University in Melbourne, Australia, found.

"Preventing weight gain, almost no matter what weight you start out at, is going to be the key to preventing knee problems," said Dr. Susan Bartlett, who has studied joint pain and obesity at McGill University in Montreal, Canada, and was not involved in the study.

Knee pain is one of the most common forms of joint pain, affecting around 18 percent of U.S. adults, according to the Centers for Disease Control and Prevention. Although the causes of the problem vary - from overuse and repetitive movement in athletes, to chronic conditions like arthritis - studies have pointed to a link between knee pain and weight gain.

Previous research has linked overweight to a higher risk of the joint disease osteoarthritis, but this is the first report to look at the role extra weight might play in knee pain, the Australian researchers say.

For the new study, they recruited 250 people ages 25 to 60 with no history of knee surgery, injury or knee joint disease. More than three quarters were women, and many were obese.

When the researchers checked in with participants two years after the study began, around a fifth had dropped out. Of the 196 people who remained, more than half had maintained their weight, while 14 percent had put on weight - about 7 kilograms, or 15 pounds, on average - and 30 percent had lost weight.

For every kilogram gained, pain scores went up by 1.9 points on a 500-point scale. Stiffness worsened by 1.4 points (on a 200 point scale), and function by 6.1 points (on a 1,700 point scale).

The study can't show with certainty that the extra pounds caused the pain, although researchers say that's likely to be the case.

"The changes might be small, but if you can put enough of these changes together, it makes the difference between having symptoms that interfere with life, and keeping them more manageable," Bartlett told Reuters Health.

The link between weight gain and pain was strongest in obese people, who experienced a 59-point increase in pain when they put on weight compared to just 6.4 points in non-obese people.

People who shed weight during the study did experience some improvement in knee pain, by 22.4 points on average. Weight loss, however, only led to a small improvement in function of 9.8 points in obese people.

In their report, published in the journal Arthritis Care and Research, Stephanie Tanamas from Monash University and colleagues say previous studies have suggested weight loss can improve knee problems. While their findings bear that out to some extent, a large drop in weight may be needed to see a benefit, the researchers add.

Bartlett did point to one limitation, however. A lot of people, especially those who lost weight, may have lost larger amounts of weight and then regained it, which may have influenced the results.

Still, she said, the study shows there is a lot of value in preventing weight gain in the first place and to some degree in losing extra pounds if you have knee problems.

"Losing weight if you are obese, and you already have arthritis, should help with symptoms and functions, but you won't be able to completely undo the effects of weight gain," Bartlett said.